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Objective By analyzing the influence of the periodic change of earth orbit on the periodic change of climate， this study examined the climate change characteristics of the Xiayoushashan Formation in Qaidam Basin and established its high-resolution astronomical scale based on Milankovitch theory to identify and divide high-frequency sequences. Methods First， the Laskar algorithm was used to calculate the variation period of the orbital parameters of Earth during the summer solstice at 35°N from 14.5-23.8 Ma， and the Miocene cycle theory and ratio in this sedimentary period were determined. Then， taking wells Xianzhong 39， Xianzhong 8-9 and Xianzhong 8-12 in the Nanbaxian oil and gas field as examples， the natural gamma data were analyzed by their frequency spectrum and continuous wavelet transform. Finally， based on the orbital period， the average sedimentation rate of the Xiayoushashan Formation was calculated， and the "floating" astronomical scale of well Xianzhong 39 was established. Results Through the analysis of frequency spectrum and continuous wavelet transform， the Neogene Xiayoushashan Formation was shown to be mainly controlled by eccentricity periods of 400 and 95 ka. The average sedimentation rate of the Xiayoushashan Formation was 0.094 41 m/ka， and the sedimentation duration was 7.2 Ma. Based on the 400 ka long and 95 ka short eccentric period curves as benchmark curves， 18 fourth-order quasi-sequence groups and 72 fifth-order quasi-sequence groups were identified. Conclusions The results show that the climate change recorded in the Xiayoushashan Formation is controlled and driven by cycles. Identification and division based on Milankovitch theory can reduce the influence of subjective factors， improve the accuracy of division results， and more accurately describe the climate change characteristics in sediments. These research results are helpful for deeply understanding the evolution law of the Warth's climate and providing important reference for oil and gas exploration and resource evaluation.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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